Trochus.] GASTROPODA. Ill 



between which are visible numerous very minute spiral striae, in the 

 interstices of which oblique incremental strise are prominently shown 

 under a lens ; base concentrically striate, the striso unequal, disap- 

 pearing toward the outer edge. Colour dull grey, whitish, or greenish. 

 Spire conic, with nearly straight outlines, ,apex acute. Protoconch very 

 small, H whorls, which have a slightly rugose surface. Whorls about 

 7, nearly planulate, or sometimes a little bulging at the upper and 

 lower margins, the last whorl strongly angled or carinate at the peri- 

 phery ; base plano-concave. Suture rather deep. Aperture suboval 

 to quadrangular, nacreous within. Outer lip convex, sharp, with a 

 smooth marginal band inside ; the outer part narrow, white, and opaque ; 

 the inner part broader, iridescent, and smooth ; further in lirate. 

 Basal lip thickened, subdentate, uniting with the columella in a regular 

 curve. Columella oblique, with a deep fold near its insertion, smooth 

 within. Umbilical area with 3 to 4 spiral ribs, interstices nacreous, 

 the umbilicus narrow and deep or partly filled up by a white callus. 

 The parietal wall transversely striate or nearly smooth, with a light- 

 brown callus. 



Diameter, 19 mm. ; height, 20 mm. 



The animal is yellowish-brown, foot reddish or purplish-brown ; 

 filaments white, 3 on each side. The head-lobes are smooth and 

 rounded, and joined together across the head. The eyes are on rather 

 long white peduncles. 



Dentition. Rutton, T.N.Z.I., xv, 124, pi. 14, f. K. 



Type CO- 



Hob. North and South Islands ; Chatham Islands : on rocky 

 ground near low-water mark. Brought to England by Captain 

 Cook. Occurs also at Norfolk Island. 



Fossil in the Pliocene. 



Subgen. 2. CLANCULUS, Montfort, 1810. 



Clanculus, Mft., Conch. Syst., 191. Type : Trochus pharaonicus, L. Clan- 

 culus, Mft., Man. Conch. (1), xi, 8, 47. Monodonta (in part), Lamarck 

 and authors. Fragella, Swainson, " Shells and Shell-fish," 352. Otavia. 

 Risso, Hist. Nat. Eur. Merid., iv, 1826, 132. Clanculopsis. Monterosato, 

 Bull. Soc. Malac. Ital., v, 1879, 222. 



Shell conical, conoidal, or turbinate ; generally granose-lirate all 

 over, periphery rounded or angular, base flat or convex, false-um- 

 bilicate ; aperture oblique, usually obstructed by teeth, the outer 

 lip usually lirate or dentate within, columella with a tooth-like fold 

 above, terminating in a tooth at the base ; false umbilicus with a 

 crenated border. 



The animal bears 4 pairs of tentacular filaments on the epipodial 

 line. The dentition is similar to that of Trochus, but the body of the 

 tooth is more expanded, the centrals and laterals bearing large lateral 

 supporting-wings. 



Distribution. Mediterranean, Indian Ocean, and Pacific. 



